1. Field of the Invention
The present invention generally relates to semiconductor devices and methods for controlling power saving.
2. Description of the Related Art
Generally, a portable phone equipped with an antenna switch semiconductor circuit has an increased number of control input terminals for operation controls as the number of ports branched increases. For example, an SP6T (single pole six through) switch has a large number of terminals including six control terminals in addition to seven RF (Radio Frequency) terminals, and has a difficulty in downsizing.
Further, there is a difficulty in layout design on a printed circuit board built in the portable phone because a large area is occupied to arrange the six control terminals in addition to the seven RF terminals. A reduced number of control terminals is needed to meet the demands of further downsizing. A decoder may be used for the purpose of further downsizing. The decoder may decodes input signals received via input terminals and outputs the original data via control output terminals.
For example, a 3-to-8 bit decoder has eight input conditions and is capable of decoding an input signal applied to three input terminals to a signal output via six output terminals. The use of the decoder makes it possible to produce the eight-bit output from the three-bit input, and reduces the number of input terminals to three. If the decoder is not used, six input terminals are needed to receive the six control signals. In some cases, the 3-to-8 bit decoder is incorporated, together with the switch, into a switch module in order to reduce the number of input terminals.
The decoder may be implemented by devices in which little standby current flows, such as CMOS (Complementary Metal Oxide Semiconductor) devices. The decoder is frequently incorporated into a GaAs switch in terms of miniaturization and cost reduction.
FIG. 1 shows a conventional switch module. Referring to FIG. 1, a switch module 1 includes a switch circuit 2 having multiple FETs (Field Effect Transistors), a decoder 3, input terminals 41 through 43, a power supply terminal 5, a ground (GND) terminal 6, an RF common terminal 7, and RF terminals 81 through 86. The switch circuit 2 and the decoder 3 are formed by GaAs devices.
FIG. 2 shows the truth table of the conventional switch module. Referring to FIG. 2, inputs 1 through 3 are signals applied to the input terminals 41 through 43, respectively. RF1-Common through RF6-Common indicate the connecting relationships between the RF common terminal 7 and the RF terminals 81 through 86. A symbol Vdd denotes a voltage applied to the power supply terminal 5. A symbol Idd denotes a statically consumed current that flows from the power supply terminal 5 to the ground terminal 6.
Each of the input signals applied to the input terminals 41 through 43 may be at either HIGH or LOW. The decoder 3 decodes the input signals, and applies decoded signals to the gates of the FETs of the switch circuit 2. The RF common terminal 7 is selectively connected to the RF terminals 81 through 86 based on the states of the FETs. The voltage Vdd applied to the decoder 3 formed by GaAs devices makes continuity between the power supply terminal 5 and the ground conduct, and causes the statically current Idd to flow statically because the decoder 3 does not have any CMOS device composed of an nMOS transistor and a pMOS transistor. Thus, power consumption cannot be reduced.